#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
int qw(int i)
{
	/*int a = 1;
	int b = 2;
	int c = 3;
	if (i == 1)
		return 1;
	if (i == 2)
		return 2;
	while (i > 2)
	{
		c = a + b;
		a = b;
		b = c;
		i--;
	}

	return c;*/
	if (i == 1)
		return 1;
	else if (i == 2)
		return 2;
	else
		return qw(i - 1) + qw(i - 2);
}
int main()
{
	int i = 0;
	scanf("%d", &i);
	printf("%d\n",qw(i));
	return 0;
}